The development of high-speed networking has traditionally been driven by the telecommunications industry and the computer industry. However the data traffic patterns for the telecommunications industry is very different from the data traffic pattern for the computer industry. Specifically, the telecommunication industry primarily has been concerned with providing data networks for carrying voice data in telephone calls. Voice data in general requires a constant bandwidth connection. Thus, the telecommunication networks were traditionally designed to provide constant bandwidth using time division multiplexing (TDM) techniques. In time division multiplexing each data stream is assigned a specific amount of bandwidth within the TDM network to transfer data. For example, synchronous optical network (SONET/SDH/PDH) is a widely used networking scheme in the telecommunications industry. SONET/SDH/PDH is a connection oriented scheme, in which each channel is given a fixed amount of bandwidth based on a standardized increment related to the amount of data needed to provide a standard voice phone call. Furthermore, TDM networks for voice-based applications are typically designed to support peak usage bandwidth requirements. Thus, under normal circumstances (i.e. non-peak usage) TDM networks are under utilized and have spare capacity.
FIG. 1 shows a typical TDM based metro area network (MAN) 100 having various network nodes 110, 120, 130, 140, 150, and 160 connected with fiber optic links 112, 121, 123, 132, 134, 143, 145, 154, 165, 156, 116, and 161. Specifically, network node 110 is coupled to network node 120 by fiber optic links 121 and 112. Fiber optic link 112 carries data from network node 110 to network node 120. Fiber optic link 121 carries data from network node 120 to network node 110. In general fiber optic link lxy carries data from network node 1x0 to network node 1y0, where x and y are in the range 1-6 inclusive. Typically, each network node provides TDM service to large number of users, who are coupled to the network node using industry standard TDM interfaces. Fiber optic links are used because of the high bandwidth, low latency, reliability, and consistency provided by fiber optic links as compared to other network medium. Metro area network 100 uses a dual ring topology. The dual ring topology provides redundancy in case one of the optical links becomes unusable. For example, if optical fiber link 123 were to become unusable, data from network node 120 could still reach network node 130 using fiber optic links 121, 116, 165, 154, and 143.
FIG. 2 is a simplified block diagram of a conventional network node 200 having a first optical interface 210, a second optical interface 220, a TDM user interface 230, and a cross connect unit 240. Optical interfaces 210 and 220 are configured to transmit and receive data with other network nodes. Specifically, each optical interface includes a fiber optic port for a transmit fiber optics link (not shown) and a receive fiber optics link (not shown). For example, if network node 200 were used in place of network node 120 (FIG. 1) optical interface 210 would be coupled to fiber optic links 112 and 121 and optical interface 220 would be coupled to fiber optics link 123 and 132. TDM user interface 230 provides an access point for receiving and transmitting data to user equipment or networks. Various embodiments of network node 200 may provide TDM user interfaces with different network medium and protocols. Data from TDM user interface 230 is transferred to optical interfaces 210 and/or 220 through cross connect unit 240. Conversely, data destined for the users of network node 200 are received by optical interfaces 210 and/or 220 and transferred to TDM user interface 230 through cross connect unit 240.
TDM networks transfer data in TDM frames like SONET, SDH, and PDH. SONET refers to Synchronous Optical Network. SDH refers to Synchronous Digital Hierarchy. PDH refers to Plesiochronous Digital Hierarchy. FIG. 3 shows an example of a TDM frame 300, which is made of header columns and payload columns. TDM frame 300 could be for example a SONET frame, a SDH frame or a PDH frame. TDM Frame 300 includes a header section 310 and payload columns such as columns 321, 325, and 327. Header section 310 contains information regarding TDM frame 300 such as the source and destination of TDM frame 300. The payload columns contain payload data to be transported. Payload data is also referred to as the transport payload. In general TDM frame 300 has a fixed number of data columns. For example, a SONET STS1 frame consists of 90 columns of 9 bytes each. The first three columns form header section 310 leaving 87 payload columns (and a byte space of 87×9 bytes) for payload. An STSn frame contains first 3×n columns of header and 87×n columns for payload. Transport payload size varies. Thus sometimes the transport payload does not occupy all of the 87n payload columns. Other times, the transport payload may spill over to a part of the payload columns of the following TDM frame. A transport payload may start at any byte in the payload columns of the TDM frame. The transport payload is packed into the payload columns in a column-wise manner and is provisioned in an integral number of columns in the TDM frame. If the TDM frame is not provisioned to full capacity, the unprovisioned columns, i.e. unused columns, are filled with dummy (non-data) characters. Thus, some of the total bandwidth of a TDM network may be unused during normal operation.
The computer industry primarily is concerned with transferring computer data over a network. In general, computer data is “bursty”, i.e., computer data traffic requires high bandwidth for some periods of times and little or no bandwidth at other times. To take advantage of high-speed networks, the computer industry adopted a packet-based approach to networking. Generally, a data stream is packetized into multiple data packets. The data packets contain identifying information so that the packets can be reassembled into the original data stream. Packet based networking allows multiple data streams to share a network and obtain better bandwidth utilization for bursty data than the TDM approach used in telecommunication networks.
With the growing use of computers and computer networks, in particular the Internet, the amount of computer data traffic is increasing very rapidly. In contrast, voice data traffic is growing at a slower pace. Furthermore, some voice data is being transformed into packet data using protocols such as Voice over Internet Protocol (VoIP). To capitalize on the growing use of packetized data, techniques and equipment need to be developed to allow efficient transport of packetized data on TDM networks having excess capacity.
Additionally, deployment limitations of typical TDM networks prevent wide spread use of TDM networks for TDM and Computer network application. As explained above, the telecommunication/computer networks make use of fiber optic links for increased bandwidth and reliability. However, installation of fiber optic cables particularly in a metropolitan area is very time consuming. For example to add fiber optic links to a new network node, trenching permits and easements must be obtained prior to installing and configuring the optical links. Including the time required to obtain permits and easements, the time to actually install and configure a fiber optic link to a new network node could be as long as 18 months. Given all the regulatory challenges and the cost of deploying fiber, fiber is deployed to only 8-10% of buildings in dense urban areas like Manhattan, N.Y. and less than 1% in dense suburban areas like San Jose, Calif. The long delay in obtaining connections to a network node cannot be tolerated in the fast paced computer industry. Hence, there is a need for a method and system to combine packet based data with TDM data and to overcome the deployment limitation of fiber optic based networks.